Getting to orbit is only the first step. Once a rocket releases its payloads, satellites still need to reach their working orbits, space stations need resupply, and ageing spacecraft need servicing or removal. That work is in-space transportation: the vehicles and services that move mass around once it is already in space.
This guide explains how in-space transportation works, the main vehicle types and propulsion technologies, the companies building them, and why logistics between orbital platforms is becoming the next layer of space infrastructure.
What is in-space transportation?
In-space transportation (sometimes called in-space mobility or space logistics) covers any movement of spacecraft or cargo that begins in orbit rather than on the ground. Typical jobs include:
- Carrying satellites from a rocket's drop-off orbit to their final operating orbit.
- Raising, lowering or changing the inclination of an orbit.
- Delivering cargo and supplies to space stations and other orbital platforms.
- Carrying spacecraft beyond Earth orbit, to the Moon or to Lagrange points.
- Docking with existing satellites to extend their life, refuel or repair them.
- Removing dead satellites and debris, or bringing hardware back to Earth.
Agencies treat it as its own discipline. The European Space Agency runs an In-Space Transportation programme, and the US FAA licenses commercial space transportation separately from launch.
Why launch is only half the journey
Rideshare missions have made launch far cheaper for small satellites, one reason the number of satellites in orbit has grown so fast. On a single flight a rocket can carry dozens of payloads, but it releases them all into roughly the same orbit, usually a sun-synchronous orbit in low Earth orbit (LEO). Customers who need a different altitude, inclination or orbital plane either accept the compromise, carry their own propulsion, or buy a ride on an orbital transfer vehicle.
This is often called the last mile delivery in space problem. It mirrors logistics on Earth: bulk transport gets cargo to a hub cheaply, and a separate network handles the final leg to each customer.
Types of in-space transportation vehicles
Orbital transfer vehicles (OTVs)
An orbital transfer vehicle rides to orbit with its customers' payloads attached, then manoeuvres to release each one at a different orbit. Most current OTVs are expendable or flown for a single mission, though reusable designs are in development.
Space tugs
“Space tug” is the broader term for a vehicle that moves other objects. The idea dates back to NASA studies in the 1970s, which proposed reusable tugs to shuttle payloads between low orbit, higher orbits and cislunar space. Today it describes OTVs, high-energy kick stages and servicing vehicles.
Satellite servicing vehicles
Servicing vehicles dock with a client satellite that is already in orbit. In 2020 Northrop Grumman's Mission Extension Vehicle (MEV-1) became the first commercial spacecraft to dock with a satellite in geostationary orbit, taking over station-keeping to extend its operating life. Newer servicers aim to refuel, repair, inspect or de-orbit their clients.
Cargo and return vehicles
Cargo vehicles resupply crewed stations, and a growing number of capsules are designed to bring experiments and manufactured products back to Earth. As commercial space stations replace the International Space Station, regular cargo flows between stations, free-flying labs and other platforms will be needed.
Space propulsion technologies
The choice of propulsion decides how fast a vehicle can move cargo and how much it can carry. The main options trade thrust against efficiency:
| Propulsion | How it works | Strengths | Trade-offs |
|---|---|---|---|
| Chemical | Burns propellants such as hydrazine or bipropellant mixes | High thrust; transfers in hours or days | Uses a lot of propellant for each manoeuvre |
| Electric (Hall-effect, ion) | Accelerates ionised propellant with electric fields, powered by solar arrays | Very propellant-efficient; ideal for large orbit changes | Low thrust; orbit raising can take weeks or months |
| Solar thermal | Heats propellant using concentrated sunlight | Higher efficiency than chemical with more thrust than electric | Newer technology with limited flight heritage |
Many vehicles combine approaches: for example, chemical thrusters for docking and fast manoeuvres, and electric propulsion for long, efficient transfers.
Companies building in-space transportation
A handful of companies have flown or are developing in-space transportation vehicles. The landscape is changing quickly, so treat this as a snapshot rather than a complete list. Our guide to space logistics companies profiles each one in more detail.
| Company | Vehicle | Focus |
|---|---|---|
| D-Orbit (Italy) | ION Satellite Carrier | Orbital transfer and payload deployment in LEO; flying since 2020 |
| Impulse Space (USA) | Mira, Helios | LEO orbital transfer (Mira) and high-energy kick stage to GEO and beyond (Helios) |
| Momentus (USA) | Vigoride | Orbital transfer and hosted payload services in LEO |
| Northrop Grumman SpaceLogistics (USA) | MEV, Mission Robotic Vehicle | Life extension and servicing for satellites in GEO |
| Starfish Space (USA) | Otter | Docking, life extension and de-orbit servicing |
| Portal Space Systems (USA) | Supernova | Highly manoeuvrable spacecraft using solar thermal propulsion |
| Orbit2Orbit | Reusable autonomous logistics vehicles | Cargo transfer between space stations, satellites and orbital platforms |
The next step: space logistics between platforms
Most of today's in-space transportation is one-way: a vehicle drops payloads off and its job is done. As commercial space stations, in-orbit manufacturing and orbital data centres come online, the need shifts to repeatable, two-way logistics: moving cargo between platforms, swapping payloads, recovering hardware and keeping infrastructure supplied.
That is the gap Orbit2Orbit's in-space logistics network is focused on. Rather than launch, the company is developing reusable, autonomous spacecraft designed to dock, deliver and redeploy multiple times, forming a logistics network between stations, satellites and orbital platforms. Development follows a staged validation path from ground testing through high-altitude near-space trials to orbital deployment.
Put simply, launch providers move mass from Earth to space. In-space logistics moves and supports those assets once they are there.
Frequently asked questions
What is in-space transportation?+
In-space transportation is the movement of spacecraft, satellites and cargo after they have already reached orbit: for example, carrying a satellite from the orbit a rocket dropped it in to the orbit it needs to operate in, or moving supplies between a space station and another platform.
What is a space tug?+
A space tug is a spacecraft designed to move other objects in orbit. It may carry payloads to a new orbit, dock with an existing satellite to extend its life, or tow a dead satellite away. Orbital transfer vehicles are a type of space tug.
What is the difference between an orbital transfer vehicle and a launch vehicle?+
A launch vehicle (rocket) lifts payloads from the ground to orbit. An orbital transfer vehicle starts its work in orbit, carrying payloads from where the rocket left them to their final destination, often over days or weeks.
What is space logistics?+
Space logistics is the planning and execution of moving, supplying, servicing and recovering assets in space. It covers in-space transportation, cargo delivery to stations, satellite servicing and refuelling, and returning hardware to Earth.
Which companies offer in-space transportation?+
Companies with orbital transfer or servicing vehicles include D-Orbit (ION Satellite Carrier), Impulse Space (Mira and Helios), Momentus (Vigoride), Northrop Grumman's SpaceLogistics (Mission Extension Vehicle), Starfish Space (Otter) and Portal Space Systems (Supernova). Orbit2Orbit is developing reusable, autonomous vehicles for moving cargo between stations, satellites and orbital platforms.
Why can't rockets deliver satellites directly to their final orbit?+
They can, but a dedicated launch is expensive. Most small satellites fly on rideshare missions that release every payload into the same orbit. A transfer vehicle lets each customer reach a different altitude or inclination without buying a whole rocket.